Liquid crystal display device

ABSTRACT

When the applied voltages are 7 V and 5 V, a transmittance of equal to or more than 50% is obtained when conditions of |2Ps·A|≦|7Clc·A| and |2Ps·A|≦|5Clc·A | are satisfied among the magnitude Ps (nC/cm 2 ) of the spontaneous polarization per unit area of the liquid crystal material, the electrode area A (cm 2 ) of the pixels and the capacity of liquid crystal Clc (nF/cm 2 ) per unit area, and a transmittance of equal to or more than 80% is obtained when conditions of |2Ps·A|≦|4.5Clc·A| and |2Ps·A|≦|3Clc·A| are satisfied thereamong. A sufficiently high transmittance is obtained without the provision of a storage capacitor.

This application is a continuation of PCT International Application No.PCT/JP2005/007410 which has an International filing date of Apr. 18,2005, which designated the United States of America.

TECHNICAL FIELD

The present invention relates to a liquid crystal display device, andmore particularly, to an active matrix driven liquid crystal displaydevice using a liquid crystal material having spontaneous polarization.

BACKGROUND ART

With the recent progression of the so-called information-orientedsociety, electronic apparatuses typified by personal computers and PDAs(personal digital assistants) have come to be widely used. The spread ofsuch electronic apparatuses has produced a demand for portableapparatuses that can be used both in offices and outdoors, and suchapparatuses are required to be reduced in size and weight. As a means ofachieving this object, liquid crystal display devices are widely used.Liquid crystal display devices are an indispensable technology not onlyfor the reduction in size and weight but also for the reduction in thepower consumption of battery driven portable electronic apparatuses.

Liquid crystal display devices are broadly classified into a reflectivetype and a transmissive type. The reflective type has a structure inwhich the light incident from the front surface of the liquid crystalpanel is reflected at the back surface of the liquid crystal panel andthe image is made visually seen by means of the reflected light. Thetransmissive type has a structure in which the image is made visuallyseen by means of the transmitted light from a light source (backlight)provided on the back surface of the liquid crystal panel. Since thereflective type in which the amount of reflected light varies dependingon the environmental condition is inferior in viewability, transmissivetype color liquid crystal display devices using color filters aregenerally used as display devices, particularly, for personal computersand the like that perform multi-color or full-color display.

At present, active driven type liquid crystal display devices usingswitching elements such as TFTs (thin film transistors) are widely usedas color liquid crystal display devices. In the TFT driven liquidcrystal display devices, although the display quality is high, since thelight transmittance of the liquid crystal panel is only approximatelyseveral percents under present circumstances, a high-brightnessbacklight is necessary to obtain high screen brightness. For thisreason, the power consumption of the backlight is increased. Inaddition, since color filters are used for color display, one pixel isnecessarily formed of three subpixels, so that high resolution isdifficult to achieve and the display color purity is insufficient.

To solve this problem, the present inventor et al. have developed fieldsequential type liquid crystal display devices (see, for example,Non-Patent Documents 1, 2 and 3). In the field sequential type liquiddisplay devices, compared with the color filter type liquid crystaldisplay devices, since no subpixel is required, higher-resolutiondisplay can be easily realized, and since the luminous colors of thelight source can be used for display as they are without the use ofcolor filters, the display color purity is excellent. Further, sincelight use efficiency is high, power consumption is low. However, torealize the field sequential type liquid crystal display devices, it isessential that the liquid crystal have a fast responsivity (equal to orless than 2 ms).

Accordingly, to achieve a fast responsivity in the field sequential typeliquid crystal display devices having excellent advantages as mentionedabove or the color filter type liquid crystal display devices, thepresent inventor et al. have researched and developed the driving of aliquid crystal such as a ferroelectric liquid crystal having spontaneouspolarization from which a fast responsivity 100 to 1000 times that ofconventional devices can be expected, by switching elements such as TFTs(see, for example, Patent Document 1). In the ferroelectric liquidcrystal, the direction of major axis of the liquid crystal moleculestilts by voltage application. A liquid crystal panel holding theferroelectric liquid crystal is sandwiched between two polarizers thepolarization axes of which are orthogonal to each other, and thetransmitted light intensity is changed by using the birefringence causedby the change of the major axis direction of the liquid crystalmolecules.

[Patent Document 1] Japanese Patent Application Laid-Open No. H11-119189

[Non-Patent Document 1] T. Yoshihara et al., ILCC 98, P1-074, issued in1998

[Non-Patent Document 2] T. Yoshihara et al., AM-LCD'99 Digest ofTechnical Papers, p.185, issued in 1999

[Non-Patent Document 3] T. Yoshihara et al., SID'00 Digest of TechnicalPapers, p.1176, issued in 2000

DISCLOSURE OF THE INVENTION

Problems to be Solved by the Invention

Although the field sequential type liquid crystal devices haveadvantages that light use efficiency is high and that power consumptioncan be reduced, to mount them on portable apparatuses, further reductionin power consumption is required. The reduction in power consumption isrequired not only of the field sequential type liquid crystal displaydevices but also of the color filter type liquid crystal displaydevices.

FIG. 1 is a schematic plan view of a conventional liquid crystal panel.As shown in FIG. 1, pixel electrodes 40 and TFTs 41 are arranged inmatrix on a glass substrate 4, and the pixel electrodes 40 are connectedto the drain terminals of the TFTs 41. The source terminals of the TFTs41 are connected to signal lines 42 drawn from a data driver 32, and thegate terminals of the TFTs 41 are connected to scanning lines 43 drawnfrom a scan driver 33. A storage capacitor 80 is provided in each pixelso as to be parallel to the pixel electrode 40 (capacity of liquidcrystal).

In the liquid crystal display devices using a liquid crystal materialhaving spontaneous polarization, since a large amount of charge isrequired for the switching of the liquid crystal, the storage capacitor80 for storing charge is typically provided in each pixel. To furtherreduce power consumption, it is effective to further increase theaperture ratio of the liquid crystal panel to thereby increasetransmittance. However, since it is necessary to provide the storagecapacitor 80 in each pixel, the aperture ratio of the liquid crystalpanel cannot be increased.

In addition, since the provision of the storage capacitor 80 increasesthe capacity of each pixel, the load on the switching elements (TFTs 41)and the driving circuits (the data driver 32 and the scan driver 33) isheavy. Therefore, the development of a liquid crystal display devicerequiring no storage capacitor is demanded.

The present invention is made in view of such circumstances, and anobject thereof is to provide an active matrix driven liquid crystaldisplay device using a liquid crystal material having spontaneouspolarization in which a sufficient transmittance is obtained andexcellent display can be provided without the provision of a storagecapacitor.

Means for Solving the Problems

A liquid crystal display device according to a first aspect is an activematrix driven liquid crystal display device having a liquid crystal cellin which a liquid crystal material having spontaneous polarization issealed, wherein a magnitude Ps (nC/cm²) of the spontaneous polarizationper unit area of the liquid crystal material satisfies a condition of|2Ps·A|≦|k·Clc·A|, and no storage capacitor is provided,

where A (cm²) is an electrode area of a pixel,

Clc (nF/cm²) is a capacity of liquid crystal per unit area, and

k is a magnitude of a voltage applied to the liquid crystal cell.

In the liquid crystal display according to the first aspect, a liquidcrystal material satisfying the condition of |2Ps·A|≦|k·Clc·A| is usedwhere Ps (nC/cm²) is the magnitude of the spontaneous polarization perunit area of the liquid crystal material, A (cm²) is the electrode areaof the pixel, Clc (nF/cm²) is the capacity of liquid crystal per unitarea and k is the magnitude of the voltage applied to the liquid crystalcell. Therefore, since the transmittance in the liquid crystal part canbe increased without the provision of a storage capacitor, excellentdisplay can be provided. Consequently, no storage capacitor is required,and since this makes it possible to increase the aperture ratio of theliquid crystal panel, the transmittance can be improved.

In a liquid crystal display device according to a second aspect, whenthe magnitude of the voltage applied to the liquid crystal cell is 7 V,the magnitude Ps of the spontaneous polarization per unit area of theliquid crystal material is equal to or less than approximately 11nC/cm².

In the liquid crystal display device according to the second aspect,when the voltage applied to the liquid crystal cell is 7 V, a liquidcrystal material the magnitude Ps of the spontaneous polarization perunit area of which is equal to or less than approximately 11 nC/cm² isused. Consequently, the condition in the first aspect can be easilysatisfied.

In a liquid crystal display device according to a third aspect, when themagnitude of the voltage applied to the liquid crystal cell is 5 V, themagnitude Ps of the spontaneous polarization per unit area of the liquidcrystal material is equal to or less than approximately 8 nC/cm².

In the liquid crystal display device according to the third aspect, whenthe voltage applied to the liquid crystal cell is 5 V, a liquid crystalmaterial the magnitude Ps of the spontaneous polarization per unit areaof which is equal to or less than approximately 8 nC/cm² is used.Consequently, the condition in the first aspect can be easily satisfied.

A liquid crystal display device according to a fourth aspect is anactive matrix driven liquid crystal display device having a liquidcrystal cell in which a liquid crystal material having spontaneouspolarization is sealed, wherein a magnitude Ps (nC/cm²) of thespontaneous polarization per unit area of the liquid crystal materialsatisfies a condition of |2Ps·A|≦|0.6·k·Clc·A|, and no storage capacitoris provided,

where A (cm²) is an electrode area of a pixel,

Clc (nF/cm²) is a capacity of liquid crystal per unit area, and

k is a magnitude of a voltage applied to the liquid crystal cell.

In the liquid crystal display device according to the fourth aspect, aliquid crystal material satisfying the condition of|2Ps·A|≦|0.6·k·Clc·A| is used where Ps (nC/cm²) is the magnitude of thespontaneous polarization per unit area of the liquid crystal material, A(cm²) is the electrode area of the pixel, Clc (nF/cm²) is the capacityof liquid crystal per unit area and k is the magnitude of the voltageapplied to the liquid crystal cell. Therefore, since the transmittancein the liquid crystal part can be increased without the provision of astorage capacitor, excellent display can be provided. Consequently, nostorage capacitor is required and since this makes it possible toincrease the aperture ratio of the liquid crystal panel, thetransmittance can be improved. In addition, compared with the firstaspect, the transmittance in the liquid crystal part can be moreincreased, so that the transmittance as the liquid crystal panel canalso be more improved.

In a liquid crystal display device according to a fifth aspect, when themagnitude of the voltage applied to the liquid crystal cell is 7 V, themagnitude Ps of the spontaneous polarization per unit area of the liquidcrystal material is equal to or less than approximately 7 nC/cm².

In the liquid crystal display device according to the fifth aspect, whenthe voltage applied to the liquid crystal cell is 7 V, a liquid crystalmaterial the magnitude Ps of the spontaneous polarization per unit areaof which is equal to or less than approximately 7 nC/cm² is used.Consequently, the condition in the fourth aspect can be easilysatisfied.

In a liquid crystal display device according to a sixth aspect, when themagnitude of the voltage applied to the liquid crystal cell is 5 V, themagnitude Ps of the spontaneous polarization per unit area of the liquidcrystal material is equal to or less than approximately 4.5 nC/cm².

In the liquid crystal display device according to the sixth aspect, whenthe voltage applied to the liquid crystal cell is 5 V, a liquid crystalmaterial the magnitude Ps of the spontaneous polarization per unit areaof which is equal to or less than approximately 4.5 nC/cm² is used.Consequently, the condition in the fourth aspect can be easilysatisfied.

In a liquid crystal display device according to a seventh aspect, ascanning time of each line in data writing scanning is a time duringwhich the liquid crystal hardly makes a response and a change intransmittance hardly occurs.

In the liquid crystal display device according to the seventh aspect, bythus setting the scanning time of each line, the active matrix driving,of the liquid crystal material having spontaneous polarization, usingswitching elements such as TFTs can be stably performed. Generally, whena response of the liquid crystal material having spontaneouspolarization occurs within the scanning time (gate on) of each line,since there is a difference in the charge consumption by the liquidcrystal at the time of gate off between when a positive voltage isapplied and when a negative voltage is applied, image sticking of thedisplay occurs. This can be prevented in the seventh aspect.

In a liquid crystal display device according to an eighth aspect, thescanning time of each line is equal to or less than 5 ps/line.

In the liquid crystal display device according to the eighth aspect, thescanning time of each line is equal to or less than 5 μs/line.Consequently, stable driving can be performed with little electric fieldresponse of liquid crystal being caused within the scanning time.Moreover, display of a large capacity of equal to or more than 560scanning lines can also be provided by the field sequential methodrequiring high-speed scanning.

The liquid crystal display device of the present invention performscolor display by the field sequential method that sequentially switchesthe lights of a plurality of colors. Consequently, the color displaywith high-resolution, high-color-purity and rapid-response can beachieved.

The liquid crystal display device of the present invention performscolor display by the color filter method using color filters.Consequently, color display can be easily performed.

The liquid crystal display device of the present invention uses a lightemitting diode as the light source for display. Consequently, switchingbetween the turning on and off of the light source can be easily made,and display color purity is improved.

EFFECTS OF THE INVENTION

According to the present invention, in the active matrix driven liquidcrystal display device using the liquid crystal material havingspontaneous polarization, since it is unnecessary to provide a storagecapacitor, the aperture ratio of the liquid crystal panel can beincreased. Consequently, light use efficiency is increased, so thatpower consumption can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic plan view of the conventional liquid crystalpanel;

FIG. 2 is a graph showing a relation between the ratio (|2Ps/Clc|) ofthe magnitude of the spontaneous polarization of the liquid crystalmaterial to the capacity of liquid crystal, and the transmittance;

FIG. 3 is a graph showing a relation between the scanning time of eachline and the transmittance in a liquid crystal display device;

FIG. 4 is a block diagram showing the circuit arrangement of a liquidcrystal display device of the present invention;

FIG. 5 is a schematic cross-sectional view of a liquid crystal panel anda backlight in a field sequential type liquid crystal display device;

FIG. 6 is a schematic view showing an example of the overall structureof the liquid crystal display device;

FIG. 7 is a schematic plan view of the liquid crystal panel of thepresent invention;

FIG. 8 is a schematic view showing an example of the structure of an LEDarray;

FIG. 9 is a view showing an example of the driving sequence in the fieldsequential type liquid crystal display device;

FIG. 10 is a schematic cross-sectional view of a liquid crystal paneland a backlight in a color filter type liquid crystal display device;and

FIG. 11 is a view showing an example of the driving sequence in thecolor filter type liquid crystal display device.

DESCRIPTION OF THE NUMERALS

7 LED array

13 liquid crystal layer

21 liquid crystal panel

22 backlight

32 data driver

33 scan driver

40 pixel electrode

41 TFT

42 signal line

43 scanning line

BEST MODES FOR IMPLEMENTING THE INVENTION

In an active matrix driven liquid crystal display device using a liquidcrystal material having spontaneous polarization according to thepresent invention, by using a liquid crystal material satisfying acondition of |2Ps·A|≦|k·Clc·A| where Ps (nC/cm²) is the magnitude of thespontaneous polarization per unit area of the liquid crystal material, A(cm²) is the electrode area of the pixel, Clc (nF/cm²) is the capacityof liquid crystal per unit area and k is the positive constant that isset in accordance with the applied voltage, a sufficient transmittancecan be realized and excellent display can be provided even when nostorage capacitor is provided. First, the value of k defined based onthe test performed by the present inventor will be described in thefollowing:

After glass substrates having transparent electrodes (electrode area: 1cm²) made of ITO (indium tin oxide) were cleaned, polyimide was appliedthereto and baked at 200° C. for one hour to thereby form polyimidefilms of approximately 200 Å. The surfaces of these films were rubbedwith a rayon cloth, the two glass substrates were placed one on anotherso that the rubbing directions were parallel to each other, and spacersmade of silica were provided between the glass substrates to hold a gap,whereby an empty panel with a gap of 1.8 μm was formed.

Ten kinds (Samples 1 to 10) of ferroelectric liquid crystal materials asshown in Table 1 shown below were each sealed in the empty panel andsandwiched between two polarizers in the crossed nicols state, wherebyten liquid crystal panels were formed. When a liquid crystal materialhaving spontaneous polarization is used, the relative dielectricconstant and the capacity of liquid crystal (Clc) exhibit frequencydependence because of the influence of the spontaneous polarization.Therefore, in the present invention, to suppress the influence ofspontaneous polarization, the relative dielectric constant and thecapacity of liquid crystal are values at a frequency of 10 kHz. TABLE 1Magnitude of spontaneous Relative Capacity of polarization × 2dielectric liquid crystal Sample No. 2Ps (nC/cm²) constant Clc (nF/cm²)Sample 1 26.5 6.3 3.1 Sample 2 28.5 6.6 3.3 Sample 3 7.7 5.9 2.9 Sample4 14.9 5.9 2.9 Sample 5 15.7 6.1 3.0 Sample 6 10.6 5.9 2.9 Sample 7 13.36.6 3.2 Sample 8 14.0 6.5 3.2 Sample 9 12.5 6.3 3.1 Sample 10 20.5 6.03.0

Then, TFTs were connected to the formed ten liquid crystal panels, andthe transmittance when a voltage was applied to the liquid crystal wasmeasured. In this case, no storage capacitor was provided. Thetransmittance was obtained by measuring the transmitted light intensityin 2.8 ms from the gate on when voltages of ±5V and ±7 V were appliedwith the gate on time being 5 μs and the interval being 2.8 ms. Atransmittance of 100% was the transmitted light intensity in theparallel nicols state. The measurement results for the liquid crystalpanels using the Samples 1 to 10 are shown in FIG. 2.

In color filter type liquid crystal display devices, even when thetransmittance of the liquid crystal is 100%, since the color filtersreduce the transmittance to ⅓, the transmittance is 33.3%. In the caseof field sequential type liquid crystal display devices, since no colorfilter is required, even when the transmittance of the liquid crystal is50%, a transmittance 1.5 times that of color filter type liquid crystaldisplay devices can be achieved. Therefore, in the present invention,50% is defined as the transmittance sufficient for display, and 80% isdefined as the more sufficient transmittance.

When the applied voltage shown at ● in FIG. 2 is 7 V, it is apparentthat to achieve a transmittance of equal to or more than 50%, acondition of |2Ps·A|≦|7Clc·A| is satisfied among the magnitude Ps(nC/cm²) of the spontaneous polarization per unit area of the liquidcrystal material, the electrode area A (cm2) of the pixel and thecapacity of liquid crystal Clc (nF/cm²) per unit area. In this case, themagnitude Ps of the spontaneous polarization is equal to or less than 11nC/cm². It is also apparent that to achieve a transmittance of equal toor more than 80%, a condition of |2Ps·A|≦|4.5Clc·A| is satisfied. Inthis case, the magnitude Ps of the spontaneous polarization is equal toor less than 7 nC/cm².

Likewise, when the applied voltage shown at Δ in FIG. 2 is 5 V, it isapparent that to achieve a transmittance of equal to or more than 50%, acondition of |2Ps·A|≦|5Clc·A| is satisfied. In this case, the magnitudePs of the spontaneous polarization is equal to or less than 8 nC/cm². Itis also apparent that to achieve a transmittance of equal to or morethan 80%, a condition of |2Ps·A|≦|3Clc·A| is satisfied. In this case,the magnitude Ps of the spontaneous polarization is equal to or lessthan 4.5 nC/cm².

While the voltages applied to the liquid crystal are 7V and 5V in theabove-described example, generally, by satisfying a condition of|2Ps·A|≦|k·Clc·A| by using the positive constant k that is set inaccordance with the voltage applied to the liquid crystal, atransmittance of equal to or more than 50% or a transmittance of equalto or more than 80% can be achieved without the provision of a storagecapacitor.

FIG. 3 is a graph showing a relation between the scanning time of eachline and the transmittance in the liquid crystal display device. Acharacteristic when the magnitude Ps of the spontaneous polarization perunit area of the liquid crystal material satisfies 2Ps=20.5 nC/cm² andthe voltage applied to the liquid crystal is 7 V is shown in FIG. 3.When the scanning time of each line is equal to or less than 5 μs/line,stable driving can be performed with little electric field response ofliquid crystal being caused within the scanning time.

The present invention will be concretely described with reference to thedrawings showing embodiments thereof. The present invention is notlimited to the embodiments shown below.

FIG. 4 is a block diagram showing the circuit arrangement of a liquidcrystal display device of the present invention. FIG. 5 is a schematiccross-sectional view of a liquid crystal panel and a backlight. FIG. 6is a schematic view showing an example of the overall structure of theliquid crystal display device. FIG. 7 is a schematic plan view of theliquid crystal panel of the present invention. FIG. 8 is a schematicview showing an example of the structure of an LED (laser emittingdiode) array serving as the light source of the backlight.

In FIG. 4, reference numerals 21 and 22 represent the liquid crystalpanel and the backlight the cross-sectional structures of which areshown in FIG. 5. As shown in FIG. 5, the backlight 22 includes an LEDarray 7 and a light directing and diffusing plate 6. As shown in FIGS. 5and 6, the liquid crystal panel 21 includes a polarizer 1, a glasssubstrate 2, a common electrode 3, a glass substrate 4 and a polarizer 5which are laminated in this order from the upper layer (front surface)side to the lower layer (back surface) side, and pixel electrodes 40arranged in matrix are formed on the common electrode 3 side surface ofthe glass substrate 4.

An alignment film 12 is disposed on the upper surfaces of the pixelelectrodes 40 on the glass substrate 4, and an alignment film 11, on thelower surface of the common electrode 3. A liquid crystal material isfilled between the alignment films 11 and 12 to form a liquid crystallayer 13. Reference numeral 14 represents spacers for holding thethickness of the liquid crystal layer 13. A driving section 50 includinga data driver 32 and a scan driver 33 is connected between the commonelectrode 3 and the pixel electrodes 40.

As shown in FIG. 7, the data driver 32 is connected to the sourceterminals of the TFTs 41 through signal lines 42, and the scan driver 33is connected to the gate terminals of the TFTs 41 through scanning lines43. The turning on and off of the TFTs 41 is controlled by the scandriver 33. The pixel electrodes 40 are respectively connected to thedrain terminal of the TFT 41. Consequently, the transmitted lightintensity of each pixel is controlled by the signal from the data driver32 that is fed through the signal line 42 and the TFT 41. In the liquidcrystal panel of the present invention, unlike the conventional example(see FIG. 1), no storage capacitor is provided, and the aperture ratiois higher than that of the conventional example in accordance with thenonprovision of a storage capacitor.

The backlight 22 is situated on the lower layer (back surface) side ofthe liquid crystal panel 21, and the LED array 7 is provided in acondition of facing an end surface of the light directing and diffusingplate 6 constituting a light emitting area. As shown in the schematicview of FIG. 8, the LED array 7 has a plurality of LEDs in which onechip is constituted by LED elements emitting light beams of threeprimary colors, that is, red (R), green (G) and blue (B), on the surfaceopposite to the light directing and diffusing plate 6. In the subframesof red, green and blue, the LED elements of red, green and blue areturned on, respectively. The light directing and diffusing plate 6functions as the light emitting area by directing light from the LEDs ofthe LED array 7 to the entire area of its own surface and diffusing thelight to the upper surface.

The liquid crystal panel 21 and the backlight 22 capable oftime-division light emission of red, green and blue are placed one onanother. The timing of turning on of the backlight 22 and the color ofthe emitted light are controlled in synchronism with the data writingscanning, based on the display data, on the liquid crystal panel 21.

In FIG. 4, reference numeral 31 represents a control signal generatingcircuit that is fed with a synchronization signal SYN from a personalcomputer and generates various control signals CS necessary for display.An image memory 30 outputs pixel data PD to the data driver 32. Based onthe pixel data PD, and the control signal CS for changing the polarityof the applied voltage, a voltage is applied to the liquid crystal panel21 through the data driver 32.

The control signal generating circuit 31 outputs the control signal CSto a reference voltage generating circuit 34, the data driver 32, thescan driver 33 and a backlight control circuit 35. The reference voltagegenerating circuit 34 generates reference voltages VR1 and VR2, andoutputs the generated reference voltages VR1 and VR2 to the data driver32 and the scan driver 33, respectively. The data driver 32 outputs asignal to the signal lines 42 of the pixel electrodes 40 based on thepixel data PD from the image memory 30 and the control signal CS fromthe control signal generating circuit 31. In synchronism with the outputof this signal, the scan driver 33 sequentially scans the scanning lines43 of the pixel electrodes 40 line by line. The backlight controlcircuit 35 feeds the backlight 22 with a driving voltage to cause thebacklight 22 to emit red light, green light and blue light.

Next, the operation of the liquid crystal display device will bedescribed. The pixel data PD for display is inputted from a personalcomputer to the image memory 30. The image memory 30 temporarily storesthe pixel data PD, and then, outputs the pixel data PD when the controlsignal CS outputted from the control signal generating circuit 31 isaccepted. The control signal CS generated by the control signalgenerating circuit 31 is fed to the data driver 32, the scan driver 33,the reference voltage generating circuit 34 and the backlight controlcircuit 35. The reference voltage generating circuit 34, when receivingthe control signal CS, generates the reference voltages VR1 and VR2, andoutputs the generated reference voltages VR1 and VR2 to the data driver32 and the scan driver 33, respectively.

The data driver 32, when receiving the control signal CS, outputs asignal to the signal lines 42 of the pixel electrodes 40 based on thepixel data PD outputted from the image memory 30. The scan driver 33,when receiving the control signal CS, sequentially scans the scanninglines 43 of the pixel electrodes 40 line by line. The TFTs 41 are drivenin accordance with the signal outputted from the data driver 32 and thescanning by the scan driver 33, a voltage is applied to the pixelelectrodes 40, and the transmitted light intensity of the pixel iscontrolled. The backlight control circuit 35, when receiving the controlsignal CS, feeds the backlight 22 with a driving voltage to cause theLED elements of red, green and blue of the LED array 7 of the backlight22 to emit light in a time-division manner so that red light, greenlight and blue light are sequentially emitted with time. In this manner,the control of turning on of each lighting area of the backlight 22emitting light that is incident on the liquid crystal panel 21, and thedata writing scanning on the liquid crystal panel 21 are synchronizedwith each other, thereby performing color display.

First Embodiment

After a TFT substrate having the pixel electrodes 40 (800×480 pixels, 4inches diagonally) without the provision of a storage capacitor and theglass substrate 2 having the common electrode 3 are cleaned, polyimideis applied thereto and baked at 200° C. for one hour to thereby formpolyimide films of approximately 200 Å as the alignment films 11 and 12.Further, these alignment films 11 and 12 are rubbed with a rayon cloth,the two substrates are placed one on another so that the rubbingdirections are parallel to each other, and the substrates are placed oneon another with the gap therebetween being held by the spacers 14 madeof silica with an average particle diameter of 1.8 μm, whereby an emptypanel is formed. A ferroelectric liquid crystal material (for example, amaterial disclosed in A. Mochizuki et al., Ferroelectrics, 133,353[1991]) the main component of which is a naphthalene-based liquidcrystal of the above-mentioned Sample 10 is sealed between the alignmentfilms 11 and 12 of the empty panel to form the liquid crystal layer 13.The magnitude (Ps) of the spontaneous polarization of the ferroelectricliquid crystal material being sealed in, which is 10.25 nC/cm², and thecapacity of liquid crystal (Clc), which is 3.0 nF/cm², satisfies thecondition of |2Ps·A|≦|7Clc·A|. The formed panel is sandwiched betweenthe two polarizers 1 and 5 in the crossed nicols state to form theliquid crystal panel 21, and setting is made so that the dark state iswhen the major axis direction of the ferroelectric liquid crystalmolecules tilt in one way.

The liquid crystal panel 21 formed in this way and the backlight 22 thelight source of which is the LED array 7 including twelve LEDs in whichone chip is constituted by LED elements emitting light beams of red (R),green (G) and blue (B) are placed one on another, and color display bythe field sequential method is performed in accordance with the drivingsequence as shown in FIG. 9. FIG. 9(a) shows the scanning timing of eachline of the liquid crystal panel 21. FIG. 9(b) shows the lighting timingof red, green and blue of the backlight 22.

One frame (period: 1/60 s) is divided into three subframes (period:1/180 s) with the frame frequency being 60 Hz, and as shown in FIG.9(a), for example, in the first subframe in one frame, writing scanningof red image data is performed twice, in the next second subframe,writing scanning of green image data is performed twice, and in the lastthird subframe, writing scanning of blue image data is performed twice.The maximum voltage applied to the liquid crystal is 7 V.

In the subframe, the time required for each data writing scanning is 25%( 1/720 s) of that ( 1/180 s) of the subframe, and the scanning time ofeach line is equal to or less than 5 μs. In each subframe, in the firstdata writing scanning (first half), a voltage of a polarity where brightdisplay is obtained is applied to the liquid crystal of each pixel inaccordance with the display data, and in the second data writingscanning (latter half), a voltage that is dissimilar in polarity andequal in magnitude to that used in the first data writing scanning isapplied to the liquid crystal of each pixel based on the display datathe same as that used in the first data writing scanning. Consequently,in the second data writing scanning, dark display that can substantiallybe regarded as black image is obtained compared with the displayobtained in the first data writing scanning.

The turning on of each of red, green and blue of the backlight 22 iscontrolled as shown in FIG. 9(b). In the first subframe, red light isemitted, in the second subframe, green light is emitted, and in thethird subframe, blue light is emitted. The backlight 22 is not always onduring the subframe, but the backlight 22 is turned on in synchronismwith the start timing of the first data writing scanning, and turned offin synchronism with the end timing of the second data writing scanning.

As a result, high-resolution, rapid-response and high-color-puritydisplay with a high transmittance can be realized.

Second Embodiment

A ferroelectric liquid crystal material (for example, a materialdisclosed in A. Mochizuki et al., Ferroelectrics, 133,353 [1991]) themain component of which is a naphthalene-based liquid crystal of theabove-mentioned Sample 9 is sealed between the alignment films 11 and 12of the empty panel formed in the process similar to that of the firstembodiment, thereby forming the liquid crystal layer 13. The magnitude(Ps) of the spontaneous polarization of the ferroelectric liquid crystalmaterial being sealed in, which is 6.25 nC/cm², and the capacity ofliquid crystal (Clc), which is 3.1 nF/cm², satisfies the condition of|2Ps·A|≦|4.5Clc·A|. The formed panel is sandwiched between the twopolarizers 1 and 5 in the crossed nicols state to form the liquidcrystal panel 21, and setting is made so that the dark state is when themajor axis direction of the ferroelectric liquid crystal molecules tiltin one way.

The liquid crystal panel 21 formed in this way and the backlight 22similar to that of the first embodiment are placed one on another, andcolor display by the field sequential method is performed in accordancewith the driving sequence as shown in FIGS. 9(a) and (b) similar to thatof the first embodiment. The maximum voltage applied to the liquidcrystal is 7 V which is the same as that of the first embodiment.

As a result, high-resolution, rapid-response and high-color-puritydisplay with a higher transmittance than that of the first embodimentcan be realized.

Third Embodiment

A monostable ferroelectric liquid crystal material (for example, R2301manufactured by Clariant Japan) is sealed between the alignment films 11and 12 of the empty panel formed by the process similar to that of thefirst embodiment, thereby forming the liquid crystal layer 13. Themagnitude (Ps) of the spontaneous polarization of the ferroelectricliquid crystal material being sealed in, which is 6 nC/cm², and thecapacity of liquid crystal (Clc), which is 3 nF/cm², satisfies thecondition of |2Ps·A|≦|5Clc·A|. After the liquid crystal material issealed in the panel, a voltage of 10 V is applied with the point oftransition from the cholesteric phase to the chiral smectic C phasebetween, whereby a uniformly aligned state of the liquid crystal isrealized. The formed panel is sandwiched between the two polarizers 1and 5 in the crossed nicols state to form the liquid crystal panel 21,and setting is made so that the dark state is when no voltage isapplied.

The liquid crystal panel 21 formed in this way and the backlight 22similar to that of the first embodiment are placed one on another, andcolor display by the field sequential method is performed in accordancewith the driving sequence as shown in FIGS. 9(a) and (b) similar to thatof the first embodiment. The maximum voltage applied to the liquidcrystal is 5 V.

As a result, high-resolution, rapid-response and high-color-puritydisplay with a high transmittance can be realized.

Fourth Embodiment

A ferroelectric liquid crystal material (for example, a materialdisclosed in A. Mochizuki et al., Ferroelectrics, 133,353 [1991]) themain component of which is a naphthalene-based liquid crystal of theabove-mentioned Sample 3 is sealed between the alignment films 11 and 12of the empty panel formed in the process similar to that of the firstembodiment, thereby forming the liquid crystal layer 13. The magnitude(Ps) of the spontaneous polarization of the ferroelectric liquid crystalmaterial being sealed in, which is 3.85 nC/cm², and the capacity ofliquid crystal (Clc), which is 2.9 nF/cm², satisfies the condition of|2Ps·A|≦|3Clc·A|. The formed panel is sandwiched between the twopolarizers 1 and 5 in the crossed nicols state to form the liquidcrystal panel 21, and setting is made so that the dark state is when themajor axis direction of the ferroelectric liquid crystal molecules tiltin one way.

The liquid crystal panel 21 formed in this way and the backlight 22similar to that of the first embodiment are placed one on another, andcolor display by the field sequential method is performed in accordancewith the driving sequence as shown in FIGS. 9(a) and (b) similar to thatof the first embodiment. The maximum voltage applied to the liquidcrystal is 5 V which is the same as that of the third embodiment.

As a result, high-resolution, rapid-response and high-color-puritydisplay with a higher transmittance than that of the third embodimentcan be realized.

While the field sequential type liquid crystal display devices aredescribed as examples in the above-described embodiments, similareffects are obtained in color filter type liquid crystal display deviceshaving color filters.

FIG. 10 is a schematic cross-sectional view of a liquid crystal paneland a backlight in a color filter type liquid crystal display device. InFIG. 10, the same parts as those of FIG. 5 are denoted by the samereference numerals, and descriptions thereof are omitted. The commonelectrode 3 is provided with color filters 60 of three primary colors(R, G and B). The backlight 22 includes a white light source 70 having aplurality of white light source elements that emit white light, and thelight directing and diffusing plate 6. In such a color filter typeliquid crystal display device, the white light from the white lightsource 70 is selectively transmitted by the color filters 60 of aplurality of colors to thereby perform color display.

By performing color display in accordance with the driving sequence asshown in FIGS. 11(a) and (b), even in the color filter type liquidcrystal display device, a sufficiently high transmittance can berealized and excellent display can be realized without the provision ofa storage capacitor as in the above-described field sequential typeliquid crystal display devices.

While cases where the ferroelectric liquid crystal materials havingspontaneous polarization are used are described in the above-describedembodiments, similar effects are obtained when other liquid crystalmaterials having spontaneous polarization such as anti-ferroelectricliquid crystal materials are used. The present invention is not limitedto transmissive type liquid crystal display devices. The presentinvention is also applicable to reflective type liquid crystal displaydevices and front/rear projectors.

With respect to embodiments including the above-described embodiments,the following additions are further disclosed:

(Addition 1)

An active matrix driven liquid crystal display device having a liquidcrystal cell in which a liquid crystal material having spontaneouspolarization is sealed, wherein a magnitude Ps (nC/cm²) of thespontaneous polarization per unit area of the liquid crystal materialsatisfies a condition of |2Ps·A|≦|k·Clc·A|, and no storage capacitor isprovided,

where A (cm²) is an electrode area of a pixel,

Clc (nF/cm²) is a capacity of liquid crystal per unit area, and

k is a positive constant that is set in accordance with a voltageapplied to the liquid crystal cell.

(Addition 2)

An active matrix driven liquid crystal display device having a liquidcrystal cell in which a liquid crystal material having spontaneouspolarization is sealed, wherein a magnitude Ps (nC/cm²) of thespontaneous polarization per unit area of the liquid crystal materialsatisfies a condition of |2Ps·A|≦|7Clc·A|, and no storage capacitor isprovided,

where A (cm²) is an electrode area of a pixel, and

Clc (nF/cm²) is a capacity of liquid crystal per unit area.

(Addition 3)

The liquid crystal display device according to Addition 2, wherein themagnitude Ps of the spontaneous polarization per unit area of the liquidcrystal material is equal to or less than 11 nC/cm².

(Addition 4)

The liquid crystal display device according to Addition 2, wherein themagnitude Ps (nC/cm²) of the spontaneous polarization per unit area ofthe liquid crystal material satisfies a condition of |2Ps·A|≦|4.5Clc·A|.

(Addition 5)

The liquid crystal display device according to Addition 4, wherein themagnitude Ps of the spontaneous polarization per unit area of the liquidcrystal material is equal to or less than 7 nC/cm².

(Addition 6)

An active matrix driven liquid crystal display device having a liquidcrystal cell in which a liquid crystal material having spontaneouspolarization is sealed, wherein a magnitude Ps (nC/cm²) of thespontaneous polarization per unit area of the liquid crystal materialsatisfies a condition of |2Ps·A|≦|5Clc·A|, and no storage capacitor isprovided,

where A (cm²) is an electrode area of a pixel, and

Clc (nF/cm²) is a capacity of liquid crystal per unit area.

(Addition 7)

The liquid crystal display device according to Addition 6, wherein themagnitude Ps of the spontaneous polarization per unit area of the liquidcrystal material is equal to or less than 8 nC/cm².

(Addition 8)

The liquid crystal display device according to Addition 6, wherein themagnitude Ps (nC/cm²) of the spontaneous polarization per unit area ofthe liquid crystal material satisfies a condition of |2Ps·A|≦|3Clc·A|.

(Addition 9)

The liquid crystal display device according to Addition 8, wherein themagnitude Ps of the spontaneous polarization per unit area of the liquidcrystal material is equal to or less than 4.5 nC/cm².

(Addition 10)

The liquid crystal display device according to any one of Additions 1 to9, wherein a scanning time of each line in data writing scanning is atime during which the liquid crystal hardly makes a response and achange in transmittance hardly occurs.

(Addition 11)

The liquid crystal display device according to Addition 10, wherein thescanning time of each line is equal to or less than 5 μs/line.

(Addition 12)

The liquid crystal display device according to any one of Additions 1 to11, wherein color display is performed by a field sequential method.

(Addition 13)

The liquid crystal display device according to any one of Additions 1 to11, wherein color display is performed by a color filter method.

(Addition 14)

The liquid crystal display device according to any one of Additions 1 to13, wherein a light source for display is a light emitting diode.

(Addition 15)

An active matrix driven liquid crystal display device having a liquidcrystal cell in which a liquid crystal material having spontaneouspolarization is sealed, wherein a magnitude Ps (nC/cm²) of thespontaneous polarization per unit area of the liquid crystal materialsatisfies a condition of |2Ps·A|≦|k·Clc·A|, and no storage capacitor isprovided,

where A (cm²) is an electrode area of a pixel,

Clc (nF/cm²) is a capacity of liquid crystal per unit area, and

k is a magnitude of a voltage applied to the liquid crystal cell.

(Addition 16)

The liquid crystal display device according to Addition 15, wherein whenthe magnitude of the voltage applied to the liquid crystal cell is 7 V,the magnitude Ps of the spontaneous polarization per unit area of theliquid crystal material is equal to or less than approximately 11nC/cm².

(Addition 17)

The liquid crystal display device according to Addition 15, wherein whenthe magnitude of the voltage applied to the liquid crystal cell is 5 V,the magnitude Ps of the spontaneous polarization per unit area of theliquid crystal material is equal to or less than approximately 8 nC/cm².

(Addition 18)

An active matrix driven liquid crystal display device having a liquidcrystal cell in which a liquid crystal material having spontaneouspolarization is sealed, wherein a magnitude Ps (nC/cm²) of thespontaneous polarization per unit area of the liquid crystal materialsatisfies a condition of |2Ps·A|≦|0.6·k·Clc·A|, and no storage capacitoris provided,

where A (cm²) is an electrode area of a pixel,

Clc (nF/cm²) is a capacity of liquid crystal per unit area, and

k is a magnitude of a voltage applied to the liquid crystal cell.

(Addition 19)

The liquid crystal display device according to Addition 18, wherein whenthe magnitude of the voltage applied to the liquid crystal cell is 7 V,the magnitude Ps of the spontaneous polarization per unit area of theliquid crystal material is equal to or less than approximately 7 nC/cm².

(Addition 20)

The liquid crystal display device according to Addition 18, wherein whenthe magnitude of the voltage applied to the liquid crystal cell is 5 V,the magnitude Ps of the spontaneous polarization per unit area of theliquid crystal material is equal to or less than approximately 4.5nC/cm².

(Addition 21)

The liquid crystal display device according to any one of Additions 15to 20, wherein a scanning time of each line in data writing scanning isa time during which the liquid crystal hardly makes a response and achange in transmittance hardly occurs.

(Addition 22)

The liquid crystal display device according to Addition 21, wherein thescanning time of each line is equal to or less than 5 μs/line.

1. An active matrix driven liquid crystal display device, comprising: aliquid crystal cell in which a liquid crystal material havingspontaneous polarization is sealed; wherein a magnitude Ps (nC/cm²) ofthe spontaneous polarization per unit area of the liquid crystalmaterial satisfies a condition of |2Ps·A|≦|k·Clc·A|, and no storagecapacitor is provided, where A (cm²) is an electrode area of a pixel,Clc (nF/cm²) is a capacity of liquid crystal per unit area, and k is apositive constant that is set in accordance with a voltage applied tothe liquid crystal cell.
 2. The liquid crystal display device accordingto claim 1, wherein a scanning time of each line in data writingscanning is a time during which the liquid crystal hardly makes aresponse and a change in transmittance hardly occurs.
 3. The liquidcrystal display device according to claim 2, wherein the scanning timeof each line is equal to or less than 5 μs/line.
 4. The liquid crystaldisplay device according to claim 1, wherein color display is performedby a field sequential method.
 5. The liquid crystal display deviceaccording to claim 1, wherein color display is performed by a colorfilter method.
 6. The liquid crystal display device according to claim1, wherein a light source for display is a light emitting diode.
 7. Anactive matrix driven liquid crystal display device, comprising: a liquidcrystal cell in which a liquid crystal material having spontaneouspolarization is sealed; wherein a magnitude Ps (nC/cm²) of thespontaneous polarization per unit area of the liquid crystal materialsatisfies a condition of |2Ps·A|≦|7Clc·A|, and no storage capacitor isprovided, where A (cm²) is an electrode area of a pixel, and Clc(nF/cm²) is a capacity of liquid crystal per unit area.
 8. The liquidcrystal display device according to claim 7, wherein the magnitude Ps ofthe spontaneous polarization per unit area of the liquid crystalmaterial is equal to or less than 11 nC/cm².
 9. The liquid crystaldisplay device according to claim 7, wherein the magnitude Ps (nC/cm²)of the spontaneous polarization per unit area of the liquid crystalmaterial satisfies a condition of |2Ps·A|≦|4.5Clc·A|.
 10. The liquidcrystal display device according to claim 9, wherein the magnitude Ps ofthe spontaneous polarization per unit area of the liquid crystalmaterial is equal to or less than 7 nC/cm².
 11. An active matrix drivenliquid crystal display device, comprising: a liquid crystal cell inwhich a liquid crystal material having spontaneous polarization issealed; wherein a magnitude Ps (nC/cm²) of the spontaneous polarizationper unit area of the liquid crystal material satisfies a condition of|2Ps·A|≦|5Clc·A|, and no storage capacitor is provided, where A (cm²) isan electrode area of a pixel, and Clc (nF/cm²) is a capacity of liquidcrystal per unit area.
 12. The liquid crystal display device accordingto claim 11, wherein the magnitude Ps of the spontaneous polarizationper unit area of the liquid crystal material is equal to or less than 8nC/cm².
 13. The liquid crystal display device according to claim 11,wherein the magnitude Ps (nC/cm²) of the spontaneous polarization perunit area of the liquid crystal material satisfies a condition of|2Ps·A|≦|3Clc·A|.
 14. The liquid crystal display device according toclaim 12, wherein the magnitude Ps of the spontaneous polarization perunit area of the liquid crystal material is equal to or less than 4.5nC/cm².
 15. An active matrix driven liquid crystal display device,comprising: a liquid crystal cell in which a liquid crystal materialhaving spontaneous polarization is sealed; wherein a magnitude Ps(nC/cm²) of the spontaneous polarization per unit area of the liquidcrystal material satisfies a condition of |2Ps·A|≦|k·Clc·A|, and nostorage capacitor is provided, where A (cm²) is an electrode area of apixel, Clc (nF/cm²) is a capacity of liquid crystal per unit area, and kis a magnitude of a voltage applied to the liquid crystal cell.
 16. Theliquid crystal display device according to claim 15, wherein when themagnitude of the voltage applied to the liquid crystal cell is 7 V, themagnitude Ps of the spontaneous polarization per unit area of the liquidcrystal material is equal to or less than approximately 11 nC/cm². 17.The liquid crystal display device according to claim 15, wherein whenthe magnitude of the voltage applied to the liquid crystal cell is 5 V,the magnitude Ps of the spontaneous polarization per unit area of theliquid crystal material is equal to or less than approximately 8 nC/cm².18. The liquid crystal display device according to claims 15, wherein ascanning time of each line in data writing scanning is a time duringwhich the liquid crystal hardly makes a response and a change intransmittance hardly occurs.
 19. The liquid crystal display deviceaccording to claim 18, wherein the scanning time of each line is equalto or less than 5 μs/line.
 20. An active matrix driven liquid crystaldisplay device, comprising: a liquid crystal cell in which a liquidcrystal material having spontaneous polarization is sealed; wherein amagnitude Ps (nC/cm²) of the spontaneous polarization per unit area ofthe liquid crystal material satisfies a condition of|2Ps·A|≦|0.6·k·Clc·A|, and no storage capacitor is provided, where A(cm²) is an electrode area of a pixel, Clc (nF/cm²) is a capacity ofliquid crystal per unit area, and k is a magnitude of a voltage appliedto the liquid crystal cell.
 21. The liquid crystal display deviceaccording to claim 20, wherein when the magnitude of the voltage appliedto the liquid crystal cell is 7 V, the magnitude Ps of the spontaneouspolarization per unit area of the liquid crystal material is equal to orless than approximately 7 nC/cm².
 22. The liquid crystal display deviceaccording to claim 20, wherein when the magnitude of the voltage appliedto the liquid crystal cell is 5 V, the magnitude Ps of the spontaneouspolarization per unit area of the liquid crystal material is equal to orless than approximately 4.5 nC/cm².